Much development is being achieved on the micrometer (μm) and nanometer (nm) size scales. For example, much work is being performed at these small size scales in such scientific fields as biology, medicine, physics, chemistry, electronics, engineering, and nanotechnology to, for example, study objects (e.g., materials, organisms, viruses, bacteria, etc.), create new objects, and/or assemble objects together with great precision.
To perform manipulation of objects on such a small size scale, it is often necessary to use microscope equipment to aid in observing the objects. For instance, the smallest object that human beings can see with the unaided eye is about 0.1 millimeter (mm). With a good light microscope (also referred to as an “optical microscope”), an image may be magnified up to about 1500 times. However, magnification achievable with light microscopes is limited by the physics of light (i.e., the wavelength of light) upon which the operation of such microscopes is based. For example, light microscopes have relatively limited resolving power (ability to distinguish clearly between two points very close together). The resolving power, a, is measured by the angular separation of two point sources that are just detectably separated by the instrument. The smaller this angle, the greater the resolving power. Thus, in general α=1.22λ/D, where λ is the wavelength of the light used and D is the diameter of the objective lens in meters (m). The best resolving power that can be achieved with a light microscope is around 0.2 μm. Points closer together than this cannot be distinguished clearly as separate points using a light microscope.
Of course, by reducing the wavelength of the radiation used in a microscope to view an object, the resolution obtainable can be improved. Thus, electron microscopes have been developed that use a beam of electrons, rather than light, to study objects too small for conventional light microscopes. Max Knoll and Ernst Ruska constructed the first electron microscope around 1930. In general, electron microscopes use a beam of electrons to irradiate a sample under study, wherein the wavelength of such electron beam (generally resulting from magnetic forces acting on the beam) is much smaller than the wavelength of light used in light microscopes. Accordingly, the amount of magnification (and the resolving power) achievable with an electron microscope is much improved over that of light microscopes.
Modern electron microscopes typically comprise: (1) an electron gun to produce a beam of accelerated electrons; (2) an image producing system that includes electrostatic lenses (e.g., generally formed by electromagnetic or permanent magnets) and metal apertures to confine and focus the electron beam, pass it through, or over, the surface of the specimen and create a magnified image; (3) an image viewing and recording system, which typically includes photographic plates or a fluorescent screen; and (4) a vacuum pump to keep the microscope under high vacuum, as air molecules may deflect electrons from their paths. The development of the electron microscope has had a massive impact on knowledge and understanding in many fields of science. Modern electron microscopes can view detail at the atomic level with sub-nanometer resolution (e.g., 0.1 nm resolution, which is 1000 times better than conventional light microscopes) at up to a million times magnification.
Various different types of electron microscopes have been developed. Such electron microscopes generally work on the above-described principles of using a directed beam of electrons, as opposed to light, for studying samples. One type of electron microscope is the transmission electron microscope (TEM). In a TEM, electrons are transmitted through a thinly sliced specimen and typically form an image on a fluorescent screen or photographic plate. Those areas of the sample that are more dense transmit fewer electrons (i.e., will scatter more electrons) and therefore appear darker in the resulting image. TEMs can magnify up to one million times and are used extensively, particularly in such scientific fields as biology and medicine to study the structure of viruses and the cells of animals and plants, as examples.
Another type of electron microscope is the scanning electron microscope (SEM). In an SEM, the beam of electrons is focussed to a point and scanned over the surface of the specimen. Detectors collect the backscattered and secondary electrons coming from the surface and convert them into a signal that in turn is used to produce a realistic, three-dimensional image of the specimen. During the scanning process, the detector receives back fewer electrons from depressions in the surface, and therefore lower areas of the surface appear darker in the resulting image. SEMs generally require the specimen to be electrically conducting. Thus, specimens that are not conducting are typically coated (e.g., using a sputter coater) with a thin layer of metal (often gold) prior to scanning. SEMs can magnify up to around one hundred thousand times or more and are used extensively, particularly in such scientific areas as biology, medicine, physics, chemistry, and engineering to, for example, study the three-dimensional (“3-D”) structure of surfaces from metals and ceramics to blood cells and insect bodies.
In addition to the above-described light and electron microscopes, various other types of microscopes have also been developed to aid in the study of micro- and/or nano-scale objects, including without limitation scanning probe microscopes (SPMs). Various types of SPMs have been developed, such as atomic force microscopes (AFMs), scanning tunnelling microscope (STM), and near field optical scanning microscope (NOSM), as examples. Microscopes have traditionally been used for imaging (e.g., viewing specimens). However, to provide greater utility, a recent trend has been to include a manipulator mechanism that may be used in conjunction with the microscope for manipulating a specimen being imaged by the microscope. For example, manipulator mechanisms, such as probes, have been developed to be integrated within an SEM for manipulating a sample being imaged by the SEM. For instance, LEO ELECTRON MICROSCOPY LTD. has proposed certain manipulating mechanisms for use with an SEM. Further, manipulator mechanisms, such as probes, have been developed to be integrated within a TEM for manipulating a sample being imaged by the TEM. For instance, NANOFACTORY INSTRUMENTS has proposed certain in situ probes for TEMs.